As a system including a plurality of servers, known is a three-layer system that includes a web server, an application (AP) server and a database (DB) server. In a system including plurality of servers, the whole system may stop due to the stopping of a part of the system.
A failure in which the whole system stops due to the stopping of a part of the system will be discussed with reference to FIGS. 12A to 12C. FIGS. 12A to 12C illustrate a three-layer system. The three-layer system 200 has a web server 210, two application servers 220 and three database servers 230. The servers have first-in-first-out (FIFO) queues, respectively. The FIFO queues hold request messages (also referred to as requests) provided from a client 240. Specifically, the web server 210 has a FIFO queue 300. The two application servers 220 have FIFO queues 310 and 320, respectively. The three database servers 230 have FIFO queues 330, 340 and 350, respectively. A request held by a queue is released by making response to the corresponding request.
The database server 230 that has the FIFO queue 340 provides information regarding a particular service S in response to a request provided from the client 240. For example, when a failure occurs in that database server 230, that database server 230 does not provide a response message (also referred to as a response) for the particular service S and the FIFO queue 340 overflows (refer to FIG. 12A). The database server 230 that has the FIFO queue 340 becomes a nonresponding state due to the overflow of the FIFO queue 340. In addition, the FIFO queues 310 and 320 of the application servers 220 that are each waiting for a response from that database server 230 overflow (refer to FIG. 12B), and the application servers 220 become a nonresponding state. Finally, the FIFO queue 300 of the web server 210 overflows, and whereby the web server 210 may not be able to receive a request from the client 240. As a result, the whole system 200 becomes a nonresponding state (refer to FIG. 12C).
Japanese Laid-open Patent Publication No. 2010-86203 discloses a related technique.